43 Columbia University Department of AstronomyÕDepartment of Physics New York, New York 10027 ͓S0002-7537͑93͒05431-9͔ This report covers the period September 1999 through astronomers, primarily amateur, who do stellar photometry August 2000 and comprises an account of astronomical with small telescopes in their backyards. Columbia personnel research carried out in the Department of Astronomy and the included Patterson, Kemp, and Locastro. They typically ob- Department of Physics. serve a star steadily for a few months, trying to amass the densest possible coverage by stressing long observation and distribution of observers in longitude. This provides a time Faculty and Research Associates were James Applegate, series well suited to the study of periodic signals, and immu- Elena Aprile, Norman Baker, William Craig, Arlin Crotts, nized from the ‘‘aliasing’’ problems inherent in data from a Karl-Ludwig Giboni, Eric Gotthelf, Charles Hailey, Jules single site. Long-time observers are in Belgium, Denmark, Halpern, David Helfand, Stephen Kahn, Marc Kamion- Maryland, Arizona, Illinois, New Zealand, South Africa, and kowski, Laura Kay ͑Barnard͒, Karen Leighly, Lloyd Motz Australia. During this period, new nodes were established in ͑Emeritus͒, Reshmi Mukherjee ͑Barnard͒, Robert Novick Finland, Canada, and California. Most programs involve the ͑Emeritus͒, Frederik Paerels, Joseph Patterson, Kevin Pren- study of cataclysmic binaries, justly famous for the many dergast, Andrew Rasmussen, Malvin Ruderman, Daniel periods present in their light curves. Savin, Edward Spiegel, Wilhelmus van der Veen, and Jac- The most interesting result came from intense coverage of queline van Gorkom and David Windt. V803 Cen, a well-known CV with a spectrum dominated by Lam Hui joined the faculty of the Physics Department and helium. It was found that V803 Cen appears to be an essen- Marcella Carollo joined the faculty of the Astronomy De- tially garden-variety dwarf nova, despite its exotica ͑ul- partment. trashort period, helium composition͒. The outbursts occur The Astronomy Department introduced a Universe Se- very often, about every 23 hr, which is why the pattern mester at the Biosphere 2 and recruited three new faculty for wasn’t noticed before ͑because this is close to the traditional the Columbia West campus, Karen Vanlandingham, Philip 24 hr sampling rate͒. They also found ‘‘superhumps’’ in the Yecko and Catherine Garmany. light curve during the star’s bright state, and managed to Graduate students participating in research were Douglas resolve the orbital and the superhump periods. The latter is Bramel, Tzu-Ching Chang, Xinzhong Chen, Jean Cottam, only 0.4% longer than P , which implies a secondary Alessandro Curioni, Akimi Fujita, Mario Jimenez-Garate, orb ͑mass-losing͒ star of only 0.014Ϯ0.009M ᭪ . Since the sec- Stefano Giovanardi, Eilat Glikman, Ming Feng Gu, JaeSub Ϫ9 ondary is now losing mass at ϳ10 M ᭪/yr, this implies that Hong, Miranda Jackson, John Keck, Tomotake Kozu, M. it is evaporating on a timescale of 107 years. Leutenegger, Yuexing Li, Kaya Mori, Nestor Mirabal, Don Large data sets, comprising typically ϳ300 hr over ϳ60 Neill, Ian Mulvany, John Peterson, Jacob Noel-Storr, Masao Sako, Joshua Spodek, Ben Sugerman, Robert Uglesich, nights, have been collected on many other short-period stars, Leven Wadley. to study accretion-disk precession in CVs. Their study and Undergraduates participating in research were Eve Arm- understanding will keep the CBA busy for years to come. strong, Miles Blanton, Maya Cohen ͑Barnard͒, Yosi Gelfand, Uglesich, Mirabal, Sugerman, and Crotts isolated a Jamila Hussain ͑Barnard͒, Eve Locastro ͑Barnard͒, Scott sample of variable stars, mostly RR Lyraes, in the core of the Schnee, Vincent Schoefer, Will Serber, Dana Stern ͑Bar- globular cluster M3, by use of the technique of image sub- nard͒, Gisela Telis, Jennie Watson-Lamprey and Debra Wil- traction. This demonstrates the extraordinary power of this lensky ͑Barnard͒. technique, in that their sample, obtained in moderate seeing Xinzhong Chen, Ming Feng Gu, and Joshua Spodek re- conditions at the ͑ground-based͒ MDM Observatory’s 1.3- ceived Ph.D. degrees. meter telescope, is more complete than a corresponding Appointments during 1999–2000 were held by Adjunct sample obtained over the same area using the Hubble Space Professors Michael Allison from GISS and Michael Shara Telescope. and Mordecai MacLow from the American Museum of Natu- Helfand, in collaboration with E. Moran ͑Berkeley͒, com- ral History, Postdoctoral Research Scientists Ehud Behar, pleted an extensive analysis of the hard X-ray luminosity per Fernando Camillo, Christina Chiappini, Valeri Egorov, O-star from young stellar populations. They show that the Christian Knigge, Uwe Oberlack, Stephen Lawrence, Louis accretion-powered binary population dominates the inte- Tao and Limin Wang. grated X-ray luminosity in the 2-10 keV band, and that the Van Gorkom continued as Chair of the Astronomy De- luminosity per O-star varies by a factor of ϳ10 among the partment, Paerels as Director of the Columbia Astrophysics galaxies of the Local Group. Contrary to previous work, the Laboratory and Kahn as Chair of the Physics Department. X-ray luminosity is not found to be a function of metallicity: the SMC and M31 have the same value. The implications of 1. STARS & STELLAR EVOLUTION these results for the contribution of starbursts to deep During 1998-2000 the activities of the Center for Back- X-ray source counts and the cosmic X-ray background are yard Astrophysics greatly expanded. This is a network of presented. 44 ANNUAL REPORT 2. X-RAY & ␥-RAY SOURCES served these from the ground using the CTIO 4-meter tele- At low Galactic latitude, establishing the nature of the scope, and confirmed them with new and archival data taken majority of the EGRET sources is a problem that continues with the Hubble Space Telescope. to require intensive multiwavelength observational effort. Gotthelf is studying several X-ray sources at the centers The Columbia group made considerable progress this year of supernova remnants in order to understand the evolution by obtaining several probable identifications. Halpern, Hel- of young neutron stars and their relationship to supernovae. fand, Gotthelf, & Leighly discovered a likely neutron-star/ Gotthelf, G. Vasisht ͑JPL/Caltech͒, and T. Dotani ͑ISAS, SNR counterpart of 3EG J2227ϩ6122 using ROSAT, Japan͒ confirmed that 1E 1841–045, the 12-s anomalous ASCA, and the VLA. An unusual feature of this source is a X-ray pulsar ͑AXP͒ which lies at the center of the supernova highly polarized radio shell with a flat radio spectrum. The remnant Kes 73, is spinning down at a remarkably rapid central X-ray counterpart is probably an energetic young pul- pace. The spin-down rate and flux are exceptionally stable; sar, estimated to be at a distance of ϳ3 kpc from its fitted these findings all but eliminate an accretion origin for the column density. Halpern, Mirabal, M. Eracleous ͑Penn State X-ray emission and strongly favor the ‘‘magnetar’’ model, U.͒, and R.H. Becker ͑U.C. Davis͒ reported a probable coun- with an enormous implied magnetic field of 7ϫ1014 G. terpart of the brightest unidentified EGRET source at inter- Along with D. Chakrabarty ͑MIT͒ and V. Kaspi ͑McGill͒, mediate latitude, 3EG J1835ϩ5918. It is a weak, ultrasoft Gotthelf and Vasisht are monitoring the long-term timing X-ray source with no optical counterpart to VϾ25, and prob- stability of the young anomalous X-ray pulsar in the SNR ably a pulsar that is either older or more distant than the Kes 73 using a set of RXTE observations. These observa- prototype, Geminga. It could be a Geminga-like pulsar, or tions span 2 years and a preliminary phase-connected timing even a recycled pulsar with a very high ␥-ray efficiency. solution confirms the remarkable spin-down stability of this Mukherjee, Gotthelf, Halpern, and Tavani identified one of object. This measurement, still in progress, will yield the all the two EGRET sources in the COS–B field 2CG 075ϩ00 important braking index thus distinguishing among various with a blazar behind the Galactic plane ͑3EG J2016ϩ3657͒. NS energy loss models and placing strong constraints on the A variable optical counterpart of this radio blazar was dis- timing noise and glitches of this young pulsar. covered, but a redshift has not yet been determined. Gotthelf discovered a 300 ms X-ray pulsar associated The MDM Observatory continues to pursue optical after- with the young Galactic supernova remnant Kes 75, one of glows of ␥-ray bursts ͑GRBs͒. Several GRBs were success- the few examples of a shell-type remnant with a central com- fully imaged in 1999–2000. Most notably, the optical after- pact radio core. This serendipitous pulsar, PSR J1846–0258, glow of the second most energetic event, GRB 991216, was was found using RXTE data originally obtained for the pur- discovered at MDM by Uglesich, Mirabal, and Kassin ͑Ohio pose of studying a nearby anomalous X-ray pulsar. The new State U.͒. Continued monitoring of its light curve revealed pulsar was subsequently located to the core of Kes 75 using jet-like behavior. The program at MDM will be intensified archival ASCA imaging data. Timing analysis implies a following the recent launch of the HETE–2 satellite, and the characteristic age of only 700 yrs, consistent with the age of increased event rate reported by the interplanetary network Kes 75, suggesting that PSR J1846Ϫ0258 is the youngest of spacecraft. A continuous update of observations of known pulsar. The rapid spin down of this pulsar is likely the GRBs at MDM Observatory is maintained at http:// result of torques from a large magnetic dipole of strength www.astro.columbia.edu/groupresearch.html. Ӎ5ϫ1013 G, just above the so-called quantum critical field. Oberlack has continued research on the interpretation of PSR J1846–0258 resides in this transitional regime where ␥ 26 -ray line emission from radioactive Al in collaboration the magnetic field is hypothesized to separate the regular with the group at MPE Garching, Germany.